1. Field of the Invention
The present invention relates to a tractor in which front wheels are supported by a suspension mechanism.
2. Description of the Related Art
Japanese Laid-open Patent Application No. 2009-255697 (JP 2009-255697 A) discloses, as a tractor configured in the manner described above, a suspension mechanism provided with: a hydraulic cylinder in which the front wheels and front axle case are supported by a traveling vehicle body so as to be capable of moving vertically, and which extends and contracts in coordination with the vertical movement of the right and left front wheels; a fluid line system for controlling the hydraulic fluid fed to and discharged from the hydraulic cylinder; and an accumulator provided to the fluid line system.
In JP 2009-255697 A, a control mode is described in which the fluid line system includes a switching valve having an orifice part that limits the flow rate of hydraulic fluid that flows to the accumulator when the hydraulic cylinder contracts, and an orifice of the switching valve is selected by the weight of an implement coupled to the traveling vehicle body, whereby the spring constant of the hydraulic cylinder is set as desired. Also, in JP 2009-255697 A, a control mode is described in which the feed and discharge of hydraulic fluid to and from the hydraulic cylinder is limited by an operation that further reduces (the cross section of) the orifice of the switching valve to suppress the vertical movement of the front part of the vehicle body when a brake operation is carried out.